Process for electrodepositing bright nickel



Patented Dec. 22,, 1931 UNITED STATES PATENT OFFICE.

warmer. 1.; rnmm, or person, AND CLYDE 0.1m wrrr, or YPSII-ANTI, incnrem, assrenoas, ZBY MESNE ASSIGNMENTS, To GENERAL srnme amen. coarom.

TION, A CORPORATION OF MICHIGAN PROCESS FOR ELECTROD'EPOSITDT G BRIGHT NICKEL Ito Drawing.

ers are made, it being understood that such reference is merely illustrative and that our invention is applicable to various other and iiifi'erent articles than the specific ones seected.

been plated heretofore, the same are usually provided with a thin or flash coating of nickel, then with acoating of cop r, and finally with a" heavier coating 0 nickel.

With the processes heretofore in general use,

it has been. found impracticable to provide a coating of nickel which does not require a large and expensive amount of buffing in order to impa" sufficient brightness to the nickel coating... While attempts have been made to produce a coating of sufiicient brightness to reduce the expense due to buff- .ing, these attempts have not met with commercial success. Furthermore, so far as we are aware, it has been impossible to obtain a bright nickel deposit upon other than a'polished surface, as distinguished from a matte surface, and, with-other than an extremely thin surface plate. Also in such processes .it has only been practical to deposit the metal at low current densities while with our process the deposition may be made with high current densities. v

We have discovered-that, by using a mate: rial quantity of lead in solution inv the electrgplating bath and by so preparing the bath an operating the process. as to insure the presence'in the nickel deposit of a much high-' er proportion of lead than has been contemplated heretofore we are enabled to produce As articles of the type referred to have Application filed "December 20, 1926. Serial No. 156,068.

a coating which possesses the brightness referred to hereinbefore and which will ssess also all of the good qualities of the st nickel-plated coatings or deposits hitherto obtained.

We obtain the foregoing general advantages, as well as others and more specific advantages to be referred to hereinafter, in and through the electroplating solution and the process of conducting the plating operation which will now beset fort Our bath and process may be convenientl employed in. connection with articles whic have been given a coating of copper, either with or without a prelimmar ash coating of nickel. If, however, a igh resistance to rustin or corrosion of the base metal is not requlred, our bath and process may be applied to the metal without a preliminary coating of any sort. I

The plating bath or solution'is prepared by dissolving the following constituentsin the respective pro ortions mentioned per gallon of the desire volume of bath or solution: 1

The solution of the foregoing ingredients will be hastened by heat, and agitation.

After all of the aforesaid ingredients have been completely dissolved and lead is shown.

to be present in solution'byftesting with sulphuric acid in a test tube, the bath or solution is substantially neutralized w1th nickel carbonate so that the pH value willhave been increased'to about 6. This will require approximately 0.41 lb. of dry nickel carbonate per gallon of such bath or-solution.

In lieuof making a single solution of the first five ingredients and neutralizing such solution later with nickel carbonate, it may .soluti ons,each containmg certain of the in-- gredients, in the proportions per gallon of desired solution specified hereinbefore, and to add one solution to the other. For instance, good results have been obtained by making a solution of the nickel sulphate, nickel chloride, and boric acid and by making a separate solution of the citric acid and basic lead carbonate, neutralizing this latter solution with nickel carbonate to the aforesaid pH Valve. Then, by mixing the solutions, the final bath will be identical in composition with the bath prepared from a single solution neutralized with nickel carbonate. After solution of the ingredients and I as a result of chemical recombinations therebetween, the bath in either instance will contain the following ingredients or substances in the respectiveproportions and normalities shown below:

We have describedtwo methods for pre- A paring the above solution but it is obvious of bath.

to one skilled in the art that a solution containing the above constituents in the proportions given maybe prepared by other methods.

Substantially pure salts for the bath and substantially pure anodes should be used.

'Tliis'will reduce to a minimum the amount ofiron and other impurities in the bath. Iron is especially undesirable, and may be removed by adding hydrogen peroxide to the bath in the proportion of approximately one gallon of eroxide to four hundred gallons uitable roportions of other oxidlzing agents may be substituted for hydrogen peroxide. The oxidizing agent will convert any ferrous iron to ferric iron," which will precipitate as ferric hydroxide in a bath .in which the acidity has been neutralized with an excess of nickel carbonate or other suitable basic compounds. The precipitated ferric hydroxide, together with other insoluble impurities, and any excess of nickel carbonate, may be removed by filtering the bath.

The addition of the oxidizing agent also has the advantage of overcoming a tendency to produce pits in the plate, which may be caused by organic materials, particularly those of glue-like nature, which may be presentin thebath. After filtration, or. before use in case the bath is not filtered,the solution should be acidified until the pH value equals 5.2 to 5.6, after which it is ready for The articles to'be plated are suspended in the bath in the usual manner. The current is passed through nickel anodes, the solution, and the articles which serve as cathodes, the cathodic current density being preferably from to amperes per square foot of surface to be coated, and the bath being maintained at a temperature of from 110 F. to 120 F.

The plating solution should be tested from time to time (preferably twice daily) in order that the acidity should be maintained substantially between pH 5.2 and 5.6. If the acidity is high, nickel carbonate (or lead carbonate if the solution is low in lead) should be added to neutralize the acid. If the solution is too alkaline, citric or sulphuric acid should be added to lower the pH value.

If the solution shows the correct acidity, but is low in lead, more lead may be added by dissolving the required'amount of basic lead carbonate in a small excess of citric acid, neutralizing-the excess citric acid with nickel carbonate, and adding to the solution this concentrated solution of lead citrate, containing nickel citrate.

. Should nickel below, nickel sulphate should be added, but only after the chloride and citrate have been brought to the required concentrations. If the chloride is low, thisshould be brought up by adding nickel chloride or a solution containing the desired amount of nickel. chloride.

If the solution is low in citrate, it may be brought up to standard by adding a pre pared solution of nickel citrate which, how ever, is not conveniently prepared of a strength greater than 2.5 normal.

Reference has been made hereinbefore to the operating tem eratures. It is advisable not to operate the ath at a temperature ma ered are those spec1fied, namely: 110 F. to 7 While a current density of 35 to 50 amperes per square foot of surface coated has been found to be very satisfactory, bright deposits have been produced at current densities varying from 5 and 70' amperes per square foot. Also, while the plating solution works best at an acidity of H 5.2 to 5.6,

good deposits have been obtaine outside this.

range. However, with'a solution of higher pH value, there is a tendency toward brittleness in the deposit and a liabality topeelat least under the current densities menhereinbefore. Furthermore, with hi her higher acidities, there is a likelihood o the deposit becoming pitted.

While the nickel concentration preferred deposits in baths wherein the nickel concentrations vary from .32 normal to 3.32 normal. As to the chloride and boric acid concentration, the concentrations set forth herein are those which have been found to be effective in operation, but these concentrations may be varied considerably by varying other conditions. It is desirable, however, to have .suflicient chloride in solution so that the nickel anode used will not become passiveat the temperature of the bath and at the current density employed. The remaining nickel is obviousl present as sulphate or citrate. Excess c loride does no harm but is more expensivethan the sulphate.

The preferred citric acid concentration, has

been hereinbefore described as 0.75 normal.

lhe function of the citric acid, which is present in the plating solution not as the free acid but as nickel citrate, is most important; it serves as a carrier for the lead, maintaining it in solution and preventing its pre cipitation as lead sulphate by the nickel sul-' .phate bath. However good results have been obtained with ra her wide variations from the-citric acid concentration referred.

to, the 0.75 normal representing a condition wherein approximately 30% of the nickel is present as citrate. Good deposits, however,

- have, been obtained with citric. acid concentrations of less than .60 normal.

The preferred lead concentration as set out herein is .053 oz. of-metallic lead per gallon, which is not much less than the solubility of lead in the solution. However, bright deposits have been obtained with about onefourth this concentration of lead. As the brightness of the deposits appears to vary with the concentration of the lead, it is desirable that this concentration be maintained near the maximum value indicated.

For the anodes, as pure nickel as'possible should be employed, it being particularly desirable that the presence of iron should be avoided, since its'co-deposition is likely to result in a deposit of inferior quality.

By preparing the bath and conducting the process in the manner described hereinbefore, we are able to produce a coating or deposit of nickel which is so bright, as compared with coatings heretofore produced, that the time required for the buffing operation is reduced to not over half of that p'reviously required and under very favorable conditions the bulfing may be altogether elim inated.

A posit thus produced is not pure nickel but an alloy of nickel and lead. Although good results have been obtained in cases where the lead constitutes. only of the alloy, it is preferred that the concentration on the solution be such that a deposit containing one or two percentof lead will be obtained. Satisamperes P91 factory deposits, containingehigher percent-' had found impossible to secure a sufliciently high proportion of lead in the deposit or plating to produce a bright effect at all comparable with that produced by the use of such a carrier. Furthermore, it has been impossible heretofore to produce such bright deposits on top of a matte deposit.

As substitutes for lead, zinc or cadmium may be used, but while these are capable of imparting brightness to the nickel deposits, theyi are much more difficult to control than lea It should be understood that, whereas we prefer to use nickel carbonate for neutralizing acidity, other compounds, such as ammonium hydroxide, sodium hydroxide, or sodium carbonate may be used. These materials will give the desired result, and the resulting ammonium or sodium salts are not harmful in small concentrations, but they do havethe disadvantage of making the bath composition more complicated and less easy to control. It will also be apparent to one skilled in the art that nickel hydrate may be substituted for an equivalent quantity of nickel carbonate.

Crystallizing of nickel citrate, and a consequent decrease of the nickel concentration, is minimized by maintaining the solution uniformly at its operating temperature, and by avoiding higher concentrations of nickel citrate than those herein mentioned as preferred Crystallizednickel citrate may be removed by filtering these solutions, -and the citrate so removed may be replaced by the addition of a freshly prepared solution of nickel citrate, which may be prepared by neutralizing citric acid with nickel carbonate.

Whereas a total nickel deposit of .0002 inch is representative of the average thickness of commercial nickel plating, we have found it possible to produce bright deposits not only of this thickness, but even to thickmesses ten times as great. But the thickness to which our bright nickel may be deposited does not appear to be limited, and we have, in fact, produced bright nickel plates in excess of .002 inch thick.

The bright nickel deposits which have been heretofore made are extremely thin deposits upon highly polished surfaces. This is in marked contrast to the behavior of our bright nickel plating solution, for We are able to plate upon a matte surface, and by continuing the deposition sufiiciently long, to obtain, finally, a. bright and lustrous surface. ,It is apparent that our process is particularly advantageous for the plating of surfaces which may be polished, but which arebufled only with diflicu'lty. These surfaces may be first platedif desired with nickel and copper from ordinary solutions and may then be finished by plating by our process, thus avoiding the necessity of bufiing, or at least producing a surface which requires very little bufling.

Having thus described ourinvention, what We claim is 1. The process of nickel plating which comprises immersing the articles to be plated in a nickel-plating bath containing at least .01 ounce of lead in each gallon of solution and a carrier for maintaining the lead in such solution, and employing with bath and articles a current having a density of from 5 to 70 amperes per square foot of surface coated.

2. The process of nickel plating which comprises immersing the articles to be coated j in a nickel plating bath containing lead and a citrate in solution, employing for the plating operation a current having'a density of from 5 to 70 amperes per square foot of surface coated, and maintaining the bath at a tempierrature of not materially less than 110 3. An electroplating bath for depositing bright nickel, the same containing lead in solution and a carrier serving to maintain the lead insolution in the presence of sulphate to the extent of at least .01 ounce per gallon of such solution.

4. An electroplating bath for depositing bright nickel, the same containing lead and nickel in solution with substantiallyone-third of the nickel present as citrate. f

5. An electroplating bath for depositing bright nickel, the same containing nickel sulphate, nickel chloride, nickel citrate, boric acid and lead citrate, the citrates being present in such proportion as .to constitute a carrier preventing the precipitation of the lead in the presence of the sulphate.

6. An electroplating bathfor depositing bright nickel, the same containing nickel sulphate, nickel chloride, nickel citrate, boric acid and lead citrate, the citrates'being present in proportion to constitute a carrier preventing the precipitation of the lead in the presence of the sulphate, and an oxidizing agent.

7. An electroplating bath for depositing bright nickel, the same being formed by solution and admixture of nickel sulphate, nickel chloride, nickel citrate, boric acid and basic lead carbonate,'the bath lthus formed being subsequently adjusted to a pH value of about 5.4 by the addition of nickel carbonate.

8. An electroplating bath, the same being formed by solution and admixture of nickel sulphate, nickel chloride, nickel citrate, boric acid and basic lead carbonate, the bath thus formed being subsequently adjusted to a pH value of about 5.4 by the addition of a basic.

nickel compound. v

9. An electroplating bath for depositing bri ht nickel comprising fol owing ingredients in the proportions mentioned per gallon of water:

1.75 lbs. nickel sulphate 0.209 lb. nickel chloride 0.238 lb. boric acid 0.437 lb. citric acid 0.067 oz. basic lead carbonate;

the bath, after complete solution of the foregoing constituents being neutralized to a pH value of 5.2 to 5.6.

10. An electroplating bath for depositing bright nickel comprising1 a solution of the fol owing ingredients in t e proportions mentioned per gallon of water:

1.75 lbs. nickel sulphate 0.209 lb. nickel chloride 0.238 lb. boric acid 0.437 lb. citric acid 0.067oz. basic lead carbonate;

the bath, after com lete solution of the foregoing constituents in neutralized to a pH value of 6 by adding t ereto approximately 0.41 lb. of dry nickel carbonate per allon and, after such neutralization, there eing added to the bath hydrogen peroxide in sufli-- cient quantity to oxidize any ferrous iron that may be present to ferric iron, and the resultant solution being filtered and acidified to a. pH value of 5.2-5.6.

11. The process of nickel plating which comprises ini'mersin the articles tobe plated in a nickel-plating hath containing from .01

to approximately .053 ounce of lead in solution per gallon of bath and a carrier for maintain-ing said amount of lead in solution, and emplqying with the bath and articles a current ensity of from 5 to am res per square foot of surface" to be coateri.

12. The-process of nickel plating which comprises immersing the articles to be plated;

signatures.

WALTER L. PINNER CLYDE C. DE WITT.

a. solution of the 

